JP4842763B2 - Optical element and optical device - Google Patents

Description

  The present invention relates to an optical element and an optical device.

  As a wave plate having a fine concavo-convex structure with a period (sub-wavelength period) shorter than the light wavelength of the used wavelength, “having a lattice pattern formed on the surface of a transparent substrate” is known. Such a wave plate exhibits optical anisotropy (structural birefringence) based on a grating pattern, and can generate a phase difference with respect to two linearly polarized light whose polarization planes are orthogonal to each other.

An important characteristic of the wave plate is “transmittance and phase difference”. It is desirable that the wave plate has not only a desired phase difference but also “high transmittance” with respect to two linearly polarized light whose polarization planes are orthogonal to each other.
The above phase difference is a function such as “refractive index of transparent substrate material” or “groove depth of grating pattern (fine concavo-convex structure)” having a sub-wavelength period. The larger the refractive index of transparent substrate material, the more the grating pattern The deeper the groove, the larger the phase difference.
However, it is not always easy to produce “a grating pattern having a sub-wavelength structure with a large groove depth” by molding or the like.

  Therefore, a “medium having a sufficiently large refractive index compared to the transparent substrate refractive index” is filled in a lattice pattern formed on the transparent substrate, and the medium having a sufficiently large refractive index compared to the transparent substrate refractive index is Patent Document 1 discloses a technique in which a “lattice pattern having the same period as the formed lattice pattern” is formed to generate a “larger phase difference”. Although this phase plate can realize a “large phase difference”, it has a medium having a sufficiently large refractive index on the transparent substrate compared to the refractive index of the transparent substrate. The amount of light reflected from the surface increases, resulting in a decrease in transmittance.

  As a method for coping with such a decrease in transmittance, a low refractive index film having a lower refractive index than the film material of the high refractive index film is further formed on the high refractive index medium filling the lattice pattern of the transparent substrate. Furthermore, what is formed is proposed (Patent Document 2).

  In this method, since light enters the low refractive index film from the air side, reflection at the interface between the air and the low refractive index film can be kept low, and the boundary between the low refractive index film and the high refractive index medium can be suppressed. Reflection on the surface can also be kept low. However, since the refractive index difference between the high refractive index medium and the transparent substrate is still large, the reflection at the interface between the high refractive medium and the transparent substrate is not reduced.

Japanese Patent Publication No. 7-99402 JP 2005-099099 A

  This invention is made | formed in view of the situation mentioned above, and makes it a subject to implement | achieve the novel optical element which can make high transmittance | permeability and desired phase difference compatible, and an optical apparatus using this optical element.

The optical element of the present invention basically has “a transparent substrate and a subwavelength structure layer”.
Although the subwavelength structure layer is provided as a thin layer on the transparent substrate, the refractive index of the material of the subwavelength structure layer is higher than the refractive index of the material of the transparent substrate.
In the sub-wavelength structure layer, a “one-dimensional lattice-like fine concavo-convex structure” is formed with a sub-wavelength period smaller than the used wavelength. The fine concavo-convex structure is formed such that the concavo-convex concave portion reaches the boundary surface between the transparent substrate and the sub-wavelength structure layer. That is, the sub-wavelength structure layer is divided in the concave / convex arrangement direction by the concave portions of the fine concave / convex structure.
The transparent substrate has “holes arranged in the same period as the one-dimensional lattice-like fine concavo-convex structure” on the sub-wavelength structure layer side. The “hole portion” communicates with the concave portion of the fine concavo-convex structure. That is, the bottom of the concave portion of the fine concavo-convex structure formed in the sub-wavelength structure layer communicates with the hole portion. As a result, as the optical element, the fine concavo-convex structure of the sub-wavelength structure layer and the arrangement of the hole portions are “one-dimensional lattices in which the concave portion of the fine concavo-convex structure and the vacant portion connected to the concave portion are formed as one unit concave structure. A grid pattern ".

The “hole portion” of the transparent substrate has a non-uniform width in the depth direction perpendicular to the boundary surface between the sub-wavelength structure layer and the transparent substrate, and the maximum width of the width is “ It is larger than the “width of the concave portion of the fine concavo-convex structure”.
With such a structure, as described later, a function of “changing the refractive index with respect to incident light” at least in the hole portion in the direction orthogonal to the boundary surface between the sub-wavelength structure layer and the transparent substrate is obtained.

  That is, at least the hole portion while ensuring the “phase difference” by the structural birefringence by the “one-dimensional lattice-like lattice pattern in which the concave portion of the fine concavo-convex structure and the hole portion connected to the concave portion is a unit of concave structure”. By changing the “refractive index for incident light” in the part of “a one-dimensional lattice-like lattice pattern in which the concave part of the fine concavo-convex structure and the hole part connected thereto are formed as one unit of concave part structure” The transmittance is improved by effectively reducing the reflection of light.

  The “cross-sectional shape in the periodic direction of the one-dimensional lattice-like fine concavo-convex structure formed in the sub-wavelength structure layer” may be, for example, a rectangular shape. In this case, the concave / convex portions of the fine concavo-convex structure of the sub-wavelength structure layer Has a uniform width in the depth direction of the recess, and the refractive index in this portion is constant in the depth direction of the recess, but the refractive index changes in the depth direction in the hole portion. Therefore, the reflection of light can be reduced.

  The “cross-sectional shape of the one-dimensional lattice-shaped fine concavo-convex structure formed in the sub-wavelength structure layer in the periodic direction” is preferably a shape in which the width of the convex portion changes in the height direction of the convex portion. . In this way, in the fine uneven structure of the sub-wavelength structure layer, when the width of the convex portion changes in the height direction, the refractive index changes in the depth direction of the concave portion also in this fine uneven structure portion. In combination with the refractive index change in the portion, the refractive index is larger in the depth direction of the above-mentioned “one-dimensional lattice-like lattice pattern in which the concave portion of the fine concavo-convex structure and the hole portion connected to the concave portion are one unit of concave structure” The gradation can be realized, an increase in reflectance due to a sudden change in the refractive index can be effectively suppressed, and the transmittance of the optical element can be further improved. The “change in refractive index” may be a continuous change or a “step-by-step change”.

  The “shape in which the width of the convex portion changes in the height direction of the convex portion” in “the cross-sectional shape in the periodic direction of the one-dimensional lattice-like fine concavo-convex structure formed in the sub-wavelength structure layer” is specifically “trapezoidal shape” It can be “shape, triangle shape, partial circle shape, or partial ellipse shape”. Of course, other shapes such as “a shape obtained by curving a triangular slope portion” can also be used.

  The triangle shape may be an equilateral triangle shape, an isosceles triangle shape, a right-angled isosceles triangle shape, or the like. The partial circular shape is “a shape forming part of a circle”, and the partial elliptical shape is “a shape forming a part of an ellipse”. Since the fine concavo-convex structure has a one-dimensional lattice shape, when the cross-sectional shape is a partial circle shape or a partial ellipse shape, the convex portion of the fine concavo-convex structure becomes “a part of a cylindrical surface or an elliptic cylinder surface”.

A sub-wavelength structure layer and the transparent substrate have different refractive index of the material, both of Ru separate der as material. The difference in refractive index between the two is not necessarily large .

Further, as a magnitude relationship between the refractive indexes of the sub-wavelength structure layer and the transparent substrate, the refractive index of the sub-wavelength structure layer is higher than the refractive index of the transparent substrate . When the sub-wavelength structure layer is formed of a high refractive index material, it is possible to realize a large phase difference while reducing the depth of the concave portion in the fine concave-convex structure having the sub-wavelength period, and it is easy to form the fine concave-convex structure.

The optical element according to any one of claims 1 to 3 can have an “optical function as a wave plate” ( claim 4 ), but “the fine concavo-convex structure of the sub-wavelength structure layer and the hole portion” The periodic structure by the periodic arrangement (the “one-dimensional lattice-like lattice pattern in which the concave portion of the fine concavo-convex structure and the hole portion connected to the concave portion are formed as one unit of concave structure”) passes through the flat portion of the surface of the transparent substrate. Thus, it is possible to form a polarization-selective diffraction grating by periodically arranging in the “uneven arrangement direction in the fine uneven structure” ( claim 5 ).

That is, in this case, “a one-dimensional lattice pattern in which the concave portions of the fine concavo-convex structure and the hole portions connected to the concave portions are formed as one unit of concave structure” is arranged on the surface of the transparent substrate at a predetermined interval. The above-mentioned grating pattern “array with a predetermined interval ” constitutes a polarization-selective diffraction grating (one grating pattern forms “one of the gratings of the diffraction grating” ). is there. Such an optical element can be used as a “polarization selective diffraction grating”.

The optical element according to any one of claims 1 to 3 can also have an optical function as a “polarizing beam splitter” ( claim 6 ).

  The transparent substrate generally has a parallel plate shape, but is not limited thereto, and may be “prism shape” or “wedge shape”. Further, the one-dimensional lattice-like fine concavo-convex structure by the sub-wavelength structure layer can be formed not only on the light incident side but also on the emission side.

The optical device of this invention has an optical element according to any one of the claims 1 to 7 (claim 7).
Such an optical device is, for example, “a projector device that guides a light beam from a light source to a liquid crystal display element and projects a display image of the liquid crystal display element on a display surface by a projection lens. The optical element according to any one of claims 1 to 6 may be arranged on the optical path between the first and second components ( Claim 8 ), or "the light beam from the light source is applied to the optical recording medium. , an optical pickup apparatus for recording and / or reproducing information by irradiating light collecting through the objective lens, the optical path between the light source and the objective lens, according to any one of claims 1 to 6 may be of the optical element is arranged "configuration (claim 9).

Here, the structural birefringence by the one-dimensional lattice-like fine concavo-convex structure having a sub-wavelength period will be briefly described.
FIG. 3A schematically shows a one-dimensional lattice-shaped fine concavo-convex structure. In this figure, the cross-sectional shape of the fine concavo-convex structure is a rectangular wave shape, that is, the cross-sectional shape of the convex portion is a rectangular shape.

  As shown in the figure, the pitch P of the fine concavo-convex structure is the width of the land of a pair of “land and space” (hereinafter referred to as “land width” as shown in the figure): a and the width of the space (hereinafter referred to as “land”). As shown in the drawing, it is referred to as “space width”): sum of b: (a + b). The height of the land with respect to the bottom of the space is defined as “groove depth: H”.

  At this time, the amount defined by “a / P” is called “filling factor”, and the amount defined by “H / a” is called “aspect ratio”. “Filling factor is large” means that land width: a occupying pitch: P is large (space width: b is small). Further, the greater the aspect ratio, the greater the groove depth: H with respect to the land width: a. The aspect ratio is preferably “less than 10”, more preferably about 5 or less, from the viewpoint of easy formation of a fine relief structure.

  When the pitch P of the fine concavo-convex structure is in the sub-wavelength order, light having a wavelength larger than the pitch P is not diffracted and is transmitted as it is as “0th order light” (the transmittance at this time is referred to as “0th order transmittance”). Is birefringent with respect to incident light.

That is, as shown in FIG. 3B, in the incident light “incident from the air region” into the fine concavo-convex structure, the polarization components that vibrate in parallel with the periodic direction of the fine concavo-convex structure (the horizontal direction in the figure): TM, land The fine concavo-convex structure acts like a “medium having a different refractive index” with respect to the polarization component TE that oscillates parallel to the longitudinal direction (direction orthogonal to the drawing).

  Assuming that the effective refractive index in the portion of the fine concavo-convex structure is n (TM) for the polarization component: TM and n (TE) for the polarization component: TE, these effective refractive indexes are those of the material on which the fine concavo-convex structure is formed. : N, the filling factor of the fine concavo-convex structure is expressed as follows using f.

n (TE) = √ {fn2 + (1-f)} (1)
n (TM) = √ [n2 / {f + (1-f) n2}] (2)
As described above, since the refractive indexes for the polarization components: TE and TM are different, the polarization component: TE is delayed in phase by “δ” as shown in FIG. 3B with respect to the polarization component: TM in the transmitted light . become.

That is, when the groove depth: H is used, the “optical thickness” of the fine concavo-convex structure is “H · n (TM)” for the polarization component: TM and “H · n” for the polarization component: TE. (TE) ", a“ phase delay: δ ”is generated according to the difference in optical thickness: H {n (TE) −n (TM)}. This “phase delay: δ” is “retardation”.
Difference in optical thickness: where H {n (TE) −n (TM)} is D and wavelength is λ, δ = 2πD / λ, but in the fine concavo-convex structure, “wavelength: wide region of λ” A substantially constant retardation "is obtained.

  n (TE) and n (TM) are determined by the refractive index: n and the filling factor: f. The retardation: δ is determined by the refractive index: n, the filling factor: f, and the groove depth: H. After all, the desired retardation can be obtained by adjusting the material (n is determined) and the form of the fine uneven structure (filling factor: f and groove depth: H are determined).

  By adjusting the retardation: δ, the phase difference with respect to the polarization components TM, TE can be set to, for example, “π or π / 2”, and various phase plates such as a half-wave plate and a quarter-wave plate can be realized. .

In the example described above, the cross-sectional shape of the convex portion of the fine concavo-convex structure is a rectangular shape, the land width: a and the space width: b are unambiguous, and the filling factor: f is also uniquely defined.
On the other hand, when the cross-sectional shape is “a trapezoidal periodic arrangement” as in the fine concavo-convex structure shown in FIG. 3C, the pitch P is unambiguous, but the width of the convex portion is the groove depth. Depending on the depth, the width: a1 and the filling factor: f1 = a1 / P in the groove depth: H1 portion, but the width: a2 and the filling factor: f2 = a2 / P in the groove depth: H2 portion. Thus, the filling factor changes in the depth direction of the groove.

  For this reason, the refractive indexes n (TE) and n (TM) given by the equations (1) and (2) “change according to the change of the filling factor”. In other words, the refractive indexes: n (TE) and n (TM) change with gradation in the depth direction of the fine concavo-convex structure.

Retardation in this case is the refractive index in the above H {n (TE) -n (TM)}: n (TE), n (TM), and average values thereof: n _M (TE), n _M (TM) The optical thickness obtained by substituting is given by “2πD / λ” where D is D.

That is, when the cross-sectional shape of the convex portion in the fine concavo-convex structure is a “shape in which the width of the convex portion changes in the height direction of the convex portion (claim 2)” like a trapezoidal shape, the refractive index: n Since (TE) and n (TM) change in the height direction of the convex portion, “high reflectance generated in the case of sudden refractive index change” is relaxed by the gradation of the refractive index, and “reflectance is reduced”. Therefore, the transmittance of 0th-order light in the fine concavo-convex structure is increased.
In the optical element of the present invention, “refractive index change at the hole” effectively reduces the reflectivity and increases the zero-order light transmittance.

  As described above, according to the present invention, a novel optical element and an optical apparatus including the optical element can be realized. The optical element of the present invention achieves both a desired phase difference and high transmittance, and therefore has good optical performance. Therefore, by using this optical element, an optical device with good performance can be realized.

Embodiments of the invention will be described below.
FIG. 1 shows a form example of the optical element.
In FIG. 1, reference numeral 10 denotes a transparent substrate, and reference numeral 20 denotes a sub-wavelength structure layer. The transparent substrate 10 and the sub-wavelength structure layer 20 are different materials and have different refractive indexes.
The case of FIG. 1A will be described as an example. The optical element in this case has a sub-wavelength structure layer 20 having a refractive index different from that of the transparent substrate 10 on the transparent substrate 10. The fine concavo-convex structure in the form of a three-dimensional lattice is formed such that the concave portion reaches the boundary surface between the transparent substrate 10 and the sub-wavelength structure layer 20 with a sub-wavelength period smaller than the used wavelength. Reference numeral 21 denotes a convex portion having a fine concavo-convex structure. Since the concave portion reaches “the boundary surface between the transparent substrate 10 and the sub-wavelength structure layer 20”, the convex portions 21 constituting the fine concavo-convex structure are separated by the concave portion on the transparent substrate.

  On the other hand, on the sub-wavelength structure layer 20 side of the transparent substrate 10, holes 11 are formed that communicate with the concave portions of the fine concavo-convex structure and are “arranged in the same period as the one-dimensional lattice-like fine concavo-convex structure”. That is, the arrangement of the hole portions 11 is “same period as the fine uneven structure of the sub-wavelength structure layer 20”.

  Since the fine uneven structure of the sub-wavelength structure layer 20 has a one-dimensional lattice shape, the cross-sectional shape of the fine uneven structure is uniform in the direction orthogonal to the drawing. In addition, the cross-sectional shape of the hole 11 is substantially uniform in the direction orthogonal to the drawing.

  In the example shown in FIG. 1A, the cross-sectional shape in the periodic direction of the one-dimensional lattice-like fine concavo-convex structure formed in the sub-wavelength structure layer 20 is such that the width of the convex portion “changes in the height direction of the convex portion”. More specifically, the cross-sectional shape is a trapezoidal shape (Claim 3).

  1B and 1C are modifications of the form shown in FIG. 1A. In the example of FIG. 1B, the bottom of the convex portion 22 in the fine concavo-convex structure of the sub-wavelength structure layer 20 is “ It forms the base portion 22A having a rectangular cross section. Further, in the example shown in FIG. 1C, the bottom of the convex portion 23 having a trapezoidal cross-sectional shape forms a “cross-sectional rectangular base 23 </ b> A” that is slightly longer than the trapezoid base.

FIG. 2 shows three examples of other forms of optical elements. In order to avoid complications, the same reference numerals as those in FIG.
In the example shown in FIG. 2A, the cross-sectional shape of the convex portion 24 of the fine concavo-convex structure formed in the sub-wavelength structure layer 20 is a triangular shape, and in the example shown in FIG. The cross-sectional shape of the convex part 25 of the fine concavo-convex structure formed is a rectangular shape, and in the example shown in (c), the cross-sectional shape of the convex part 26 of the fine concavo-convex structure formed in the sub-wavelength structure layer 20 is a partial circular shape. It is.

  In the three examples shown in FIG. 1 and the two examples shown in FIGS. 2A and 2C, the width of the convex portion of the fine concavo-convex structure formed in the sub-wavelength structure layer 20 “changes in the height direction of the convex portion”. Therefore, as described with reference to FIG. 3C, the refractive index also changes in a gradation even in the fine concavo-convex structure itself.

  As described with reference to the embodiment shown in FIGS. 1 and 2, the optical element of the present invention communicates with the concave portion of the fine concavo-convex structure on the sub-wavelength structure layer 20 side of the transparent substrate 10. Holes 11 arranged in the same cycle as the three-dimensional lattice-like fine concavo-convex structure are formed. And since this void | hole part has "the function to change the refractive index with respect to incident light in the direction (vertical direction of FIG. 1, FIG. 2) orthogonal to the interface surface of the transparent substrate 10 and the subwavelength structure layer 20,". is there.

Here, as an example of the material of the transparent substrate / sub-wavelength structure layer constituting the optical element, the material of the transparent substrate 10 is quartz (refractive index: n = 1.45) or trade name: BSC7 manufactured by HOYA. (N = 1.5) is preferred.
The sub-wavelength structure layer 20 is formed of a material having a higher refractive index than these, and includes “inorganic materials such as TiO ₂ , Nb ₂ O ₅ , Ta ₂ O ₅ , ZrO ₂ , ITO (SnO ₂ + In ₂ O ₅ ). ”,“ Sol-gel material ”in which elements such as TiO ₂ , ZrO ₂ , Sb ₂ O ₅ , ITO, Al ₂ O ₃ are combined in the material, and further in the sol-gel material having SiO ₂ as a skeleton In addition, a “mixed material” in which fine particles (5 nm to 100 nm) of the inorganic material are dispersed, or a photo-curing resin or a thermosetting resin having a refractive index of 1.6 or more can be used.

  The above “mixed material” can be mixed and blended according to the characteristics. As the photocurable resin or thermosetting resin, for example, “excellent optical characteristics” including a light transmitting adhesive is used. The sub-wavelength structure layer formed of the “inorganic material” has a heat resistance of 200 ° C. or more, and is suitable as “a material for a sub-wavelength structure layer of an optical element used in a high temperature environment”.

In the following, the case where the transparent substrate 10 is a parallel plate of quartz (refractive index: n = 1.45) and the sub-wavelength structure layer 20 is Ta ₂ O ₅ (refractive index: n = 2.25) is taken as an example. explain.

A subwavelength structure layer made of Ta ₂ O ₅ is formed as a thin layer on a flat surface of a parallel plate of quartz as the transparent substrate 10 by a film formation technique such as sputtering or vapor deposition.

  When the sub-wavelength structure layer 20 is formed of the sol / gel material, mixed material, photo-curing resin or thermosetting resin, these are formed on the transparent substrate 10 on a thin layer by spin coating or the like. That's fine.

  The “one-dimensional lattice-like fine concavo-convex structure having a sub-wavelength period” formed on the sub-wavelength structure layer 20 is, for example, “a latent image is formed by scanning an electron beam on the sub-wavelength structure layer formed as a thin layer. The resist layer is provided, and a pattern corresponding to the fine concavo-convex structure is drawn on the resist layer by an electron beam to form a latent image, which is developed to form a resist pattern corresponding to the fine concavo-convex structure. The subwavelength structure layer can be formed by etching to the surface of the transparent substrate 10 by etching such as RIE (reactive ion etching) using this resist pattern as a mask.

When such an etching method is used, the etching rate varies depending on the material.
By utilizing this “difference in etching rate”, it is possible to form the hole 11 as shown in FIGS. In general, since a high refractive index material has a characteristic that it is difficult to be etched by etching, the etching of the “sub-wavelength structure layer 20 by the high refractive index material (Ta ₂ O ₅ )” is etched to the boundary with the transparent substrate 10. When the etching is further performed, the transparent substrate 10 is etched by the concave portions of the fine concavo-convex structure formed in the sub-wavelength structure layer 20, so that the void portions 11 are formed. In this way, the hole 11 that is “connected to the concave portion of the fine concavo-convex structure” is formed in the transparent substrate 10.

  The size and cross-sectional shape of the hole 11 can be controlled by switching or adjusting the etching conditions (type and amount of introduced gas, etching time, etc.) according to the material of the transparent substrate / subwavelength structure layer, By controlling the cross-sectional shape and size of the cavity 11, the change in refractive index in the hole is controlled to reduce “loss of transmittance due to reflection at the interface between the sub-wavelength structure layer 20 and the transparent substrate 10”. It becomes possible to do.

  FIG. 4A shows a part of the embodiment shown in FIG. In this embodiment, the convex portion 21 of the fine concavo-convex structure has a trapezoidal cross-sectional shape, and as described above, the refractive index also changes in the vertical direction of the figure even in this fine concavo-convex structure portion.

  In addition, since the arrangement of the hole portions 11 also constitutes “one kind of fine uneven structure”, structural birefringence also occurs in this portion, but the cross-sectional shape of the hole portion 11 is not uniform. Even in the portion, the “fill factor changes in the depth direction of the hole 11” causes a change in the refractive index. This gradation of refractive index change reduces the reflectance.

  The “reflectance reduction effect due to the change in refractive index in the hole portion 11” is mainly divided into four quantities characterizing the size and shape of the hole portion 11, that is, as shown in FIG. Pitch of the concavo-convex structure: P (this is also the arrangement pitch of the hole portions 11), the maximum width in the arrangement direction of the hole portions 11: X, the depth of the hole portions 11: H2, and the maximum in the hole portions 11 It has become clear through the inventors' research that the depth: giving X: substantially determined by Z.

Therefore, the state of FIG. 4 (a) is “modeled as a polygonal cross-sectional shape” shown in FIG. 4 (b), and in order to see the effect of reducing the reflectivity due to the change in the refractive index, transmission to the polarization components: TM and TE is performed. The rate was investigated by arithmetic simulation.
The prerequisites for the operation simulation are as follows.

The transparent substrate 10 is a quartz parallel plate and has a refractive index: n = 1.45, Ta ₂ O ₅ of the sub-wavelength structure layer 20, and a refractive index: n = 2.25.
In the calculation, an amount having a length dimension was normalized by the wavelength used: λ and made non-dimensional.

  That is, the pitch of the fine concavo-convex structure: P / λ = 0.5, the width of the convex portion at the bottom of the trapezoidal shape that is the cross-sectional shape of the convex portion in the fine concavo-convex structure: 0.7 P / λ = 0.35, Width: 0.3 P / λ = 0.15, height of convex portion (depth of concave portion): H1 / λ = 0.74.

Under such conditions, as calculation parameters,
Depth of hole portion: H2 / λ, Maximum width in hole portion 11: Depth giving X: Z: Depth of gap portion: H2 ratio: Z / H2 These parameters: H2 / Various changes were made in λ and Z / H2, and the “maximum width of hole portion: ratio of X and pitch: P: change in 0th-order light transmittance with respect to change in X / P” was examined. The results are shown in FIGS.

The vertical axis “Efficiency” in each of FIGS. 5 and 6 represents the 0th-order light transmittance, and when no vacancy is formed (on the flat surface of the transparent substrate, “fine irregularities of the subwavelength structure layer” Polarized component when “only structure” exists: TE transmittance is 1. That is, this case is “when there is no effect of the hole portion”, and the transmittance of the polarization component: TM at this time is 0.92.
In FIGS. 5 and 6, “with and without cavities” means “with and without voids” and “TE-OT” with the 0th-order light transmittance of polarization component: TE. "TM-OT" represents the 0th-order light transmittance of the polarization component: TM.

  As shown in FIGS. 5 and 6, the 0th-order light transmittance: TE-OT is “smaller than the case where there is no hole portion” due to the presence of the hole portion, but it is sufficient in a region where X / P is large. With regard to the transmittance: TM-OT, “larger value than in the case where there is no hole” can be realized by the size of X / P.

  Next, regarding retardation, the above parameters: H2 / λ is set to 0.25 and 0.49, and parameters: Z / H2 is set to 0.0 (when there is no hole), 0.2, 0.4, 0.6 When the wavelength is changed to 0.8, 1.0, the change in the retardation parameter: X / P in units of λ is obtained as shown in FIGS. 7A and 7B. It was. The vertical axis “Retardation” in FIG. 7 is retardation.

  As is clear from FIG. 7, there is a “depth of the void portion: the retardation tends to increase as H2 increases”. In the example in the description, the refractive index of the sub-wavelength structure layer is higher than that of the transparent substrate, and the influence of the fine concavo-convex structure on the retardation is greater than the influence of the hole portion.

  From the above results, it is desired to achieve high transmittance by adjusting the depth of the concave portion (height of the convex portion): H1 and the depth of the void portion: H2 in the fine concavo-convex structure by controlling the etching conditions. The phase difference can be realized.

  For example, if the optical element is realized as a quarter-wave plate, the quarter-wave plate corresponds to retardation: 0.25λ. Therefore, the depth of the hole portion: H2 is made shallower than in the case of FIG. X / P may be selected such that the retardation is 0.25λ.

  As is apparent from the above explanation, the 0th-order light transmittance of the optical element is that the cross-sectional shape of the convex portion of the fine concavo-convex structure in the sub-wavelength structure layer is trapezoidal (the width changes in the height direction of the convex portion). The “refractive index gradation in the fine concavo-convex structure” and “refractive index gradation in the hole” contribute to the improvement of the 0th-order light transmittance (reduction of reflectivity) of the optical element. However, if there is “a change in the refractive index at least in the hole portion”, the transmittance can be improved.

  In addition, if necessary, a part or all of the vacant part, or further, part or all of the concave portion of the fine concavo-convex structure in the depth direction may be lower than the lower refractive index of the transparent substrate / subwavelength structure layer. Alternatively, a material having a lower refractive index may be filled.

  If the optical element is realized as a “half-wave plate”, the retardation may be set to 0.5λ, and the fine concavo-convex structure / hole portion may be set so as to realize the retardation: 0.5λ. However, instead of doing this, subwavelength structure layers are formed on both sides of a parallel plate-like transparent substrate, and both sides are formed with a fine concavo-convex structure / hole array, with a retardation of 0.25 on each side. H2 and X / P may be set. In this way, the aspect ratio of the fine concavo-convex structure can be set to be smaller than that in which the retardation: 0.5λ is realized only on one side.

Further, when the sub-wavelength structure layer is formed only on one surface of the transparent substrate, the transmittance can be further improved by forming an antireflection film on the other surface of the transparent substrate. As the antireflection film, for example, a well-known “four-layer structure in which high refractive index layers and low reflectance layers are alternately laminated” or the like can be formed by vapor deposition.
The optical element 30 according to the embodiment shown in FIG. 8 is a “polarization selective diffraction element”.
The polarization selective diffraction grating 30 has a configuration as shown in FIG. In other words, reference numeral 31 in the figure indicates a transparent substrate.
FIG. 8B is an enlarged view of the “optical element surface portion” indicated by reference numeral 33 in FIG. As shown in FIG. 8B, the “fine concavo-convex structure by the arrangement of the convex portions 321 and the periodic structure by the periodic arrangement of the hole portions 311 (portion indicated by reference numeral 32 in FIG. 8A)” is the surface of the transparent substrate 31. Are periodically arranged in the concave / convex arrangement direction (left / right method in the drawing) of the fine concave / convex structure through the flat portion 31A to form a “diffraction grating”. That is, the individual periodic structures 32 indicated by reference numeral 32 in FIG. 8A correspond to “individual gratings of the diffraction grating” ( claim 5 ).

  The polarization selective diffraction element 30 is a “polarization dependent diffraction grating”. When the phase difference between the light wave passing through the periodic structure 32 and the light wave passing through the flat portion 31A is 2π, the diffracted wave is a 0th-order transmitted wave. Further, when the phase difference is π, there is no 0th-order transmitted wave, and all diffracted waves are 1st-order or higher. By utilizing the optical anisotropy in the periodic structure 32, the polarization component: TE (vibration plane is parallel to the drawing) and the phase difference: 2π ", the polarization component: TM (vibration plane is orthogonal to the drawing). When “fine concavo-convex structure and hole arrangement are set” so as to give “phase difference: π”, a polarization selective diffraction element in which the polarization component: TE wave passes and the polarization component: TM is all diffracted is obtained.

  Even in such a polarization-selective diffraction element, the presence of the hole portion has an effect of “reducing reflectance loss”.

The optical element 40 shown in FIG. 9 is a “polarization beam splitter” ( claim 6 ). The polarizing beam splitter 40 has a fine concavo-convex structure formed in the sub-wavelength structure layer formed on the transparent substrate in the same manner as described with reference to FIGS. 1 and 2, and communicates with the concave portion of the fine concavo-convex structure. A periodic array of holes is formed on the transparent substrate side. The cross-sectional shape of the convex portion of the fine concavo-convex structure can be various shapes as exemplified in FIGS.

  In a diffractive element in a scalar region (grating pitch is sufficiently larger than the wavelength) formed by an isotropic uniform medium, the diffraction efficiency does not exhibit polarization dependence, but the grating structure has a fine uneven structure and pitch. In the sub-wavelength region, optical anisotropy depending on the grating structure, that is, structural birefringence appears, so that the diffraction efficiency becomes polarization dependent. Therefore, the function of the “polarization beam splitter” can be given to the fine uneven structure.

  In the example of FIG. 9, for example, the polarization component: TM is transmitted straight as 0th order light, and the polarization component: TE is diffracted as first order diffracted light. If the diffraction angle is set to 45 degrees with respect to the optical element 40, the zero-order light (polarization component: TM) and the first-order diffracted light (polarization component: TE) are separated so as to be orthogonal to each other as shown in the figure. can do. Also in this case, the presence of the hole portion produces an effect of “reducing reflectance loss”.

In the following, an embodiment of an optical apparatus using the optical element of the present invention will be described.
The optical device shown in FIG. 10 is a projector device ( claim 8 ).
Three liquid crystal display elements 110, 111, and 112 that individually form images of the respective colors corresponding to the three primary colors, and a cross prism 113 that combines the image lights of the respective colors emitted from these liquid crystal display elements, Wavelength plates 116, 117, and 118 are provided in the three optical paths between the cross prism 113. As the wave plates 116, 117, and 118, the wave plates corresponding to the half wave plates described in the above embodiment are used.

  White light emitted from the white light source 101 is reflected by the reflector 102 and enters the dichroic mirror 103. The dichroic mirror 103 transmits light having a blue wavelength or less and reflects light having a wavelength longer than the blue wavelength. Accordingly, of the white light incident on the dichroic mirror 103, the blue component is transmitted through the dichroic mirror 103, and the green component and the red component are reflected by the dichroic mirror 103 and incident on the dichroic mirror 104.

  The dichroic mirror 104 transmits light having a wavelength longer than the red wavelength and reflects light having a wavelength shorter than the red wavelength. Accordingly, among the light incident on the dichroic mirror 104, the green component is reflected by the dichroic mirror 104 and the red component is transmitted through the dichroic mirror 104. In this manner, the white light from the white light source 101 is color-separated by the dichroic mirrors 103 and 104 into three primary color component lights of red, green, and blue.

  The “blue component light” transmitted through the dichroic mirror 103 is reflected by the mirror 105 and enters the liquid crystal display element 110, and the “green component light” reflected by the dichroic mirror 104 enters the liquid crystal display element 111. The “red component light” transmitted through the dichroic mirror 104 follows the optical path formed by the relay lens 108, the mirror 106, the relay lens 109, and the mirror 107 and enters the liquid crystal display element 112. The relay lenses 108 and 109 perform optical path length correction for red component light.

The liquid crystal display elements 110, 111, and 112 have “a liquid crystal layer sandwiched between a pair of polarizers”, and the pair of polarizers sandwiching the liquid crystal layer have their polarization directions orthogonal to each other.
Each color component light becomes linearly polarized light and enters the liquid crystal layer when passing through the incident side polarizer of the corresponding liquid crystal display element. Image signals are applied to the liquid crystal display elements 110, 111, and 112 so as to display a blue image, a green image, and a red image, respectively, and light transmitted through the liquid crystal layer at the position of “image pixels to be projected” is polarized. The surface rotates 90 degrees, and has the same polarization direction as that of the exit-side polarizer and passes through the exit-side polarizer.

  In this way, the liquid crystal display element 110 emits “blue component light that is two-dimensionally intensity-modulated in accordance with a blue image (hereinafter referred to as“ blue image light ”). Similarly, the liquid crystal display element 111 emits “green component light that is two-dimensionally intensity-modulated in accordance with a green image (hereinafter referred to as“ green image light ”), and the liquid crystal display element 112 emits a“ red image. Accordingly, red component light (hereinafter referred to as “red image light”) that is two-dimensionally intensity-modulated is emitted. That is, the liquid crystal display elements 110, 111, and 112 individually form images corresponding to the three primary colors (blue, green, and blue).

Each color image light emitted from each liquid crystal display element has a polarization direction parallel to the plane of the drawing.
The blue image light emitted from the liquid crystal display element 110 is incident on the wave plate 116, and the green image light and red image light emitted from the liquid crystal display elements 111 and 112 are incident on the wave plates 117 and 118, respectively.

  The wave plates 116, 117, and 118 are “corresponding to a half-wave plate” and give a phase difference of ½ wavelength to two orthogonal components of transmitted light. Since each color image light incident on these wave plates is polarized in a plane parallel to the drawing as described above, the transmitted light is rotated 90 degrees from the direction in which the polarization plane is incident, and in a direction orthogonal to the drawing. It becomes a polarized light beam and enters the cross prism 113 from the corresponding surface.

  The cross prism 113 is a rectangular parallelepiped made of a light-transmitting material having a square cross-sectional shape when viewed from a direction orthogonal to the drawing, and has reflection surfaces 113a and 113b orthogonal to each other. The reflective surface 113a is “a dichroic mirror that reflects light having a wavelength less than or equal to the blue wavelength and transmits light having a wavelength longer than the blue wavelength”, and the reflective surface 113b is “reflects light having a wavelength greater than or equal to the red wavelength, It is a “dichroic mirror that transmits light having a wavelength shorter than the red wavelength”.

  Of the color image lights incident on the cross prism 113, the blue image light is reflected on the reflection surface 113a, the red image light is reflected on the reflection surface 113b, and the green image light is transmitted through the reflection surfaces 113a and 113b. The colors are synthesized and emitted from the cross prism 113. The emitted light beam is incident on the projection lens 114 and is enlarged and projected on the screen 115 which is a “display surface” by the projection lens 114 to display a projected image.

  The reflecting surfaces 113a and 113b have directionality with respect to the “polarization axis of reflected light or transmitted light”, and generally have “higher transmittance in one polarization direction”. Therefore, in order to optimize the polarization direction of the incident light to the cross prism 113 and the polarization axis of the reflecting surface, wave plates 116, 117, and 118 corresponding to half-wave plates are inserted in front of the cross prism 113. In this embodiment, the case where wave plates 116, 117, and 118 corresponding to half-wave plates are inserted into the blue, green, and red color image lights is shown, but only one of the image lights is shown. It is good also as a structure which inserts the said wavelength plate with respect to.

  FIG. 11 is a modification of the embodiment shown in FIG. In order to avoid complications, the same reference numerals as those in FIG. 10 are given to those that are not likely to be confused, and the description of FIG.

  The projector apparatus of FIG. 11 is obtained by adding a uniform illumination unit 201 (optical integrator) and a polarization conversion element 202 between the white light source 101 and the dichroic mirror 103 of the projector apparatus of FIG.

  The uniform illumination means 201, which is an “optical integrator”, is a means for making the amount of light irradiated to the liquid crystal display element substantially uniform. For example, a well-known device composed of, for example, a fly-eye lens, a rod lens, a rectangular lens array, etc. it can.

  The polarization conversion element 202 is used to effectively use the light from the white light source 101 and align the polarization direction of the light incident on the liquid crystal display element in order to brighten the projected image on the screen.

  The liquid crystal display elements 110, 111, and 112 utilize the polarization characteristics of the liquid crystal and can achieve high contrast. However, since the liquid crystal is sandwiched between a pair of polarizers, the embodiment shown in FIG. As described above, when the irradiation light incident on each liquid crystal display element is in a naturally polarized state, half of the amount of illumination light is blocked when passing through the “incident side polarizer” of each liquid crystal display element. As a result, the light utilization efficiency is poor.

  The polarization conversion element 202 converts the polarization state of the illumination light from the light source side from “natural polarization state to linear polarization state while substantially preserving the light intensity of the illumination light”. If the polarization direction of the linearly polarized illumination light is aligned with the polarization direction of the incident-side polarizer in the liquid crystal display element, approximately 100% of the illumination light from the light source side can be used for displaying a projected image. Can do.

  FIG. 12 is a diagram for explaining a state in which the white light beam from the light source is made uniform by the uniform illumination unit 201 and the polarization state is converted by the polarization conversion unit 202.

  The white light beam from the light source side is transmitted through a known uniform illumination unit 201 “configured by arranging a pair of condensing lens arrays (fly-eye lens arrays) to face each other” and enters the polarization conversion unit 202. The polarization conversion means 202 has an optical base 202A and a wave plate portion 202B.

As shown in FIG. 12A, the portion of the optical base 202A has a polarization separation surface 2021 and a reflection surface 2022 inclined by 45 degrees with respect to the optical axis of the illumination light.
The polarization separation surface 2021 divides incident light into reflected light S (hereinafter referred to as “S component”) and transmitted light P (hereinafter referred to as “P component”) whose polarization surfaces are orthogonal to each other. The reflecting surface 2022 reflects the S component and directs it in the direction substantially the same as the traveling direction of the P component.

  The combination of the polarization separation surface 2021 and the reflection surface 2022 is one unit, and a plurality of such units are provided over the transmission region of the illumination light to form a so-called “polarization prism lens array”, and the individual elements constituting the array For each polarizing prism, the transmitted illumination light is divided into an S component and a P component.

  The wave plate portion 202B rotates the polarization plane of the S component emitted from the optical substrate 202A by 90 degrees and aligns it with the polarization direction of the P component. In this way, “linearly polarized illumination light having a uniform polarization direction” is obtained. The polarization direction of the illumination light is of course the same as “the polarization direction of the incident-side polarizer of each liquid crystal display element”.

  FIG. 12B is a view for explaining the wave plate portion 202B. The wavelength plate portion 202B has a sub-wavelength of a fine concavo-convex structure 2021B, 2022B, 2023B and the like having a rectangular cross section on the surface of a thin layer 202B2 made of “material having a refractive index of 1.6 or more” formed on one surface of a glass plate 202B1 Each of the fine concavo-convex structures 2021B is provided with a function as a “wave plate equivalent to a half-wave plate”. The glass flat plate 202B1 is integrated with “a surface on the side where illumination light with a uniform direction is emitted” in the optical base 202A, and the fine concavo-convex structure 2021B and the like are formed on “a portion where the S component is emitted”. The wave plate portion 202B and the optical base body 202A may be joined with the thin layer 202B2 on the side of the optical base body 202A. In this way, the fine uneven structure can be better protected by the glass flat plate 202B1.

  Further, the thin layer 202B2 may be directly formed on the optical base 202A without using the glass flat plate 202B1. The wave plate described in the first embodiment may be used as the wave plate portion 202B used in the present embodiment. Of course, the fine concavo-convex structure 2021B, 2022B, 2023B having a rectangular cross section formed on the surface of the thin layer 202B2 formed on one surface of the glass flat plate 202B1 is formed so that the concave portion reaches the glass flat plate 202B1. The 0th-order light transmittance in the wave plate portion can be increased by connecting the holes to the glass plate so that the holes are formed in the glass flat plate.

  FIG. 13 shows a modification of another embodiment of the projector apparatus.

  This projector device is a “single plate type”, and projects a illuminating device 300 that emits white light, a “liquid crystal display device” that modulates the emitted white light to form a color image, and a displayed color image. A projection lens 309 is included.

  The lighting device 300 includes a substrate 302, an LED chip 301 that is mounted on the substrate 302 and emits white light, and “rod” as an illuminance distribution uniformizing means for uniformizing the illuminance distribution of light emitted from the LED chip 301. A lens 303, a filler 304a, a reflective layer 305, and a wave plate 306 ". The filler 304 a is formed of “a material having a higher refractive index than the rod lens 303”, and fills the space between the LED chip 301 and the boundary surface 304 formed as a concave surface on the surface of the rod lens 303 on the LED chip 301 side. Has been. The wave plate 306 provided on the light emission side end face 303b of the rod lens 303 is equivalent to a quarter wave plate.

  The “liquid crystal display device” includes a liquid crystal display element 380A, a polarizer 308a and a color filter 308c disposed on the incident side thereof, and a polarizer 308b disposed on the exit side. In the polarizers 308a and 308b, the directions of polarization planes of light to be transmitted (referred to as polarization directions) are orthogonal to each other. The color filter 308c performs “color separation of white light into three primary colors of red, green, and blue”.

  The LED chip 301 emits white light when supplied with power. The emitted white light propagates in the filler 304 a and enters the boundary surface 304 with the rod lens 303 and enters the rod lens 303. Since the filler 304 a has a refractive index higher than that of the rod lens 303, the white light is refracted so as to approach the optical axis direction (left-right direction in the drawing) of the rod lens 303 at the boundary surface 304.

  The white light propagating in the rod lens 303 propagates while repeating total reflection on the wall surface of the rod lens 303, and the illuminance distribution on the light emitting side end face 303b is made uniform by repeating total reflection.

  White light emitted from the light emission side end face 303 b of the rod lens 303 is incident on the quarter wavelength plate 306. Since the white light emitted from the LED chip 301 is “randomly polarized light”, it transmits the ¼ wavelength 306 as random polarized light. This white light is incident on the polarizer 308a, and the p-polarized component parallel to the polarization direction of the polarizer 308a is transmitted as it is, and is incident on the liquid crystal display element 308A via the color filter 308c.

The s-polarized component orthogonal to the polarization direction of the polarizer 307a is reflected by the polarizer 307a, reenters the quarter-wave plate 306, and is converted into, for example, “clockwise circularly polarized light” and propagates through the rod lens 303. Then, the light is reflected by the reflective layer 305 formed on the LED chip side surface 303a of the rod lens 303, and enters the polarizer 307a again through the rod lens 303. When reflected by the reflective layer 305, the clockwise circularly polarized light is converted into “counterclockwise circularly polarized light”, enters the quarter-wave plate 306, is converted into a p-polarized component, and passes through the polarizer 307a. The light enters the liquid crystal display element 308A through the color filter 308c.
In this way, most of the white light emitted from the LED chip 301 is incident on the color filter 308c efficiently and with a uniform illuminance distribution, and the color filter 308c changes the color to the three primary colors red, green, and blue. After being decomposed and rotated by the liquid crystal display element 308A according to the image information, the plane of polarization is rotated, and when the light passes through the polarizer 308b, it becomes color image light and is projected onto the screen 310 by the projection lens 309 to form a color projection image.

  This projector device is a “single-plate projector device” having a single illumination device 300 having an LED chip 301 that emits white light, a color filter 308c, and a single liquid crystal display device. Can be implemented.

  In this embodiment, the LED chip 301 that emits white light is provided. Instead, three types of LED chips that emit red, green, and blue light may be used. As described above, when three LED chips that emit red, green, and blue color light are arranged instead of the LED chip 301, the “color filter 81 may be used to simultaneously emit three LED chips simultaneously”. “The three LED chips may be cyclically emitted without using the color filter 308c. This eliminates the need for the color filter 308c, thereby further reducing the cost of the projector apparatus. .

  In this projector apparatus, a wave plate 306 corresponding to a quarter wave plate and polarizers 307a and 307b are used. As the wave plate and polarizer, the retardation described above: a wave plate of 0.25λ and a polarization plate are used. A beam splitter can be used.

  FIG. 14 shows a modification of another embodiment of the projector apparatus.

This projector apparatus uses a reflective liquid crystal display element.
The light source device is the same as that of FIG. 13, and includes an LED 410 that emits white light, a rod lens 411, and the like. The white light whose illuminance distribution is made uniform by the rod lens 411 is transmitted through the polarizer 413 through the wave plate 412 corresponding to the quarter wave plate, and is reflected by the joint surface of the polarization beam splitter 414 to be a reflective liquid crystal display element. 415 is incident.

  The reflective liquid crystal display element 415 performs “spatial modulation that rotates the polarization plane of incident light” in accordance with a video signal. In this embodiment, a “liquid crystal on silicon (LCOS) element capable of high-speed switching is used. The reflected light converted into p-polarized light based on the video signal is transmitted through the polarization beam splitter 414, enters the projection lens 416 as image light, and is enlarged and projected on the screen 417.

  As the polarizer 413 and the polarizing beam splitter 414 used in this embodiment, the above-described polarizing beam splitter (FIG. 9) and the above-mentioned retardation: 0.25λ are used as the wave plate 412 corresponding to a quarter wave plate. Wavelength plates can be used.

  FIG. 15 is a diagram for explaining an optical pickup device which is an embodiment of the optical device. The optical pickup device 500 sequentially transmits light emitted from a light source 502 such as a semiconductor laser through a diffraction grating 503, a polarization beam splitter 504, a quarter wavelength plate 505, a collimator lens 506, and an objective lens 507, and an optical recording medium 509. The reflected light (returned light) is incident on the polarization beam splitter 504 via the objective lens 507 and the quarter wavelength plate 505 and reflected toward the cylindrical lens 510. The return light given astigmatism by the cylindrical lens 510 is detected as read data or the like by the photodetector 511.

  The polarization selective diffraction element (FIG. 8) as the diffraction grating 503, the polarization beam splitter (FIG. 9) as the polarization beam splitter 504, and the retardation: 0.25λ wave plate as the quarter wavelength plate 5. Can be used.

It is a figure for demonstrating the embodiment of an optical element. It is a figure for demonstrating another example of implementation of an optical element. It is a figure for demonstrating the structural birefringence by a fine uneven structure. It is a figure for demonstrating the optical function of the optical element of this invention. It is a figure for demonstrating the optical function of an optical element. It is a figure for demonstrating the optical function of an optical element. It is a figure for demonstrating the optical function of an optical element. It is a figure for demonstrating one Embodiment of a polarization selective diffraction grating. It is a figure for demonstrating one Embodiment of a polarization beam splitter. It is a figure explaining one Embodiment of the projector apparatus as an optical apparatus. It is a figure explaining another form of implementation of the projector apparatus as an optical apparatus. It is a figure for demonstrating the uniform illumination means and polarization conversion means of the projector apparatus of FIG. It is a figure explaining the other form of implementation of the projector apparatus as an optical apparatus. It is a figure explaining the other form of implementation of the projector apparatus as an optical apparatus. It is a figure explaining one Embodiment of the optical pick-up apparatus as an optical apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Transparent substrate 20 Subwavelength structure layer 11 Hole part 21 Convex part of fine concavo-convex structure

Claims (9)

On the transparent substrate, it has a sub-wavelength structure layer with a thin layer having a higher refractive index than the transparent substrate,
In the sub-wavelength structure layer, a one-dimensional lattice-like fine concavo-convex structure is formed such that the concave portion reaches a boundary surface between the transparent substrate and the sub-wavelength structure layer, with a sub-wavelength period smaller than the used wavelength.
The transparent substrate has, on the sub-wavelength structure layer side, vacancy portions that communicate with the concave portions of the fine concavo-convex structure and are arranged in the same cycle as the one-dimensional lattice-like fine concavo-convex structure,
The void portion has a non-uniform width in the depth direction orthogonal to the boundary surface, and the maximum width of the width is the fine uneven structure at the boundary surface position between the sub-wavelength structure layer and the transparent substrate. An optical element characterized by being larger than the width of the recess . The optical element according to claim 1, wherein
An optical element characterized in that the cross-sectional shape in the periodic direction of the one-dimensional lattice-like fine concavo-convex structure formed in the sub-wavelength structure layer is a shape in which the width of the convex portion changes in the height direction of the convex portion. The optical element according to claim 2, wherein
An optical element, wherein a cross-sectional shape in a periodic direction of a one-dimensional lattice-like fine concavo-convex structure formed in a sub-wavelength structure layer is a trapezoidal shape, a triangular shape, a partial circular shape, or a partial elliptical shape. The optical element according to claim 1, 2 or 3,
An optical element having an optical function as a wave plate . The optical element according to any one of claims 1 to 3,
A periodic structure based on the periodic arrangement of the fine concavo-convex structure of the sub-wavelength structure layer and the holes is periodically arranged in the concavo-convex arrangement direction of the fine concavo-convex structure through the flat portion of the surface of the transparent substrate. An optical element comprising a diffraction grating . The optical element according to any one of claims 1 to 3,
An optical element having an optical function as a polarizing beam splitter . An optical device comprising the optical element according to claim 1 . The optical device according to claim 7.
It is configured as a projector device that guides a light beam from a light source to a liquid crystal display element, and projects a display image of the liquid crystal display element on a display surface with a projection lens,
An optical device according to any one of claims 1 to 6, wherein an optical element according to any one of claims 1 to 6 is disposed on an optical path between the light source and the projection lens . The optical device according to claim 7 .
It is configured as an optical pickup device that records and / or reproduces information by condensing and irradiating a light beam from a light source onto an optical recording medium via an objective lens,
An optical device according to any one of claims 1 to 6 , wherein an optical element according to any one of claims 1 to 6 is disposed on an optical path between the light source and the objective lens.

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